Conventionally, in mobile communication systems for mobile telephones or the like, the transmission power over radio communication between a base transceiver station and a mobile communication terminal is controlled. Such a transmission power control is generally provided in accordance with the line quality. For instance, in a case where there is a short distance between the mobile communication terminal and the base transceiver station, the line quality is comparatively excellent and the transmission power is kept low. This also keeps battery reduction low and decreases the interference to another communication terminal. Conversely, in a case where there is a long distance between the mobile communication terminal and the base transceiver station, that is a case where the mobile communication terminal is located at an end of a service area, the line quality is ensured by increasing the transmission power. In this manner, by increasing or decreasing the transmission power in accordance with the line quality, the line quality of the mobile communication terminal is ensured and the battery duration is also elongated.
As a method of controlling the transmission power to ensure the line quality, a technique described in, for example, Patent Document 1 or Patent Document 2 is known.
The aforementioned Patent Document 1 describes a method of, when a decrease in the propagation path gain is detected at a first radio communication device, the transmission power of a second radio communication device is decreased, and when an increase in the propagation path gain is detected at the first radio communication device, the transmission power of the second radio communication device is increased. Thus, a desired line quality is attained while suppressing an increase in the average transmission power.
In addition, the aforementioned Patent Document 2 describes a method of detecting a transmission success rate at the transmission side and increasing or decreasing the transmission power to make the transmission success rate fall within an allowable range, so that the transmission output power is decreased to the minimum level at which the line quality can be kept.    Patent Document 1: JP 2005-51819 A    Patent Document 2: JP 2006-165742 A